1. Field of the Invention
The present invention relates generally to air purifiers, and more specifically to bipolar ionization tubes for use in heating, ventilation and cooling (HVAC) systems to reduce the number of air particulates.
2. Description of the Related Art
Indoor air environments frequently include suspended particulates, such as dust, dander, soot and smoke particles, pollen, mold, bacteria, and viruses. Indoor gases are also present, being released from building materials, home furnishings and nondurable goods. In office environments, the greater user of machines, such as photocopying equipment and the like, is especially problematic, as this equipment may emit volatile organic compounds.
These particulates can degrade the quality of the air, making it less pleasant and even dangerous to occupants of the space. Modern construction techniques that promote energy efficiency, such as insulating walls, ceilings, doors and windows, and wrapping buildings with air intrusion barriers, have created spaces that are so airtight that the buildings are unable to off-gas toxic elements.
In ordinary heating, ventilation and cooling (HVAC) systems, air is drawn through a filter, which is intended to trap particulates in the filter. However, traditional filters are only effective for large particles of at least 10 microns in size. While high efficiency particle air (HEPA) filters are more effective, they also have disadvantages, as they may quickly become clogged, requiring frequent changing to avoid overburdening the HVAC equipment. Because of the presence of contaminants in the air and the general inability of physical filters to remove the same, a condition known as “sick building syndrome” has developed. Various building codes designed to mitigate this syndrome have been introduced; for example, the American Society of Heating, Refrigeration & Air Conditioning Engineers (ASHRAE) recommends a minimum of 8.4 air exchanges in a 24-hour period (a 35% turnover rate). While commercial and industrial facilities generally meet that minimum level, their air quality may remain inferior. Furthermore, there are many houses that do not even meet such minimum levels. While greater turnover rates would increase the interior air quality, they would also reduce the buildings' energy efficiencies.
An alternative method to filtering involves the use of ion exchange technology to remove contaminants from air. Ionization occurs where an atom or group of atoms loses or gains one or more electrons. An electrically neutral atom or molecule will have an equal number of electrons and protons. If an electron bound to an atom or molecule absorbs enough energy from an external source, it may exceed the ionization potential and allow the electron to escape its atomic orbital. When this occurs, the electron is lost, and an ion with a positive electrical charge, a cation, is produced. Electrons that are lost become free electrons. When a free electron later collides with an atom, it may be captured within an orbital. The gain of an electron by an atom or molecule creates an ion with a negative electrical charge, an anion.
The ionization of air, e.g., air in the Earth's atmosphere, results in the ionization of the air's constituent molecules, primarily oxygen and nitrogen. While the nitrogen in air is more plentiful than oxygen, oxygen is more reactive. Thus, oxygen has a lower ionization potential than nitrogen, allowing for oxygen cations to be formed with greater ease than nitrogen cations, and oxygen has a higher electro-negativity than nitrogen, allowing for oxygen anions to be formed with greater ease than nitrogen anions.
Ionization is known to break down organic chemicals into the basic molecular constituents of water, carbon dioxide, and related metal oxides. Thus, ionization has potential for cleaning indoor air, by eliminating organic molecules and their associated odors from the enclosed environment. Ionization also contributes to the reduction of inorganic pollutants, by imparting a charge to those molecules, which clump together and then drop out of the air.
Studies indicate that positive ions (cations) may impair human health in a number of ways, such as by stimulating increased production of the neurohormone serotonin, which may lead to exhaustion, anxiety and depression. Positive ions are frequently found in offices where VDUs (visual display units) are used. Negative ions (anions) have a calming effect. Thus, a machine that cleans indoor air should seek to introduce negative ions into the airstream.
Various commercial products have been made including machines that incorporate bipolar ionization tubes. The ionization of air may also produce ozone, O3, which is not desirable. Therefore, there is demand for a system which provides a sufficient level of ionization to effectively address the contaminants in an airstream, while minimizing the production of ozone.
Under the circumstances, it would be highly desirable to use ion exchange technology for air treatment, and indeed there are many suppliers of bipolar ionization tubes that are stand alone devices used in specified locations, or centralized installations which are integrated into a building HVAC system. These devices are used in a way so that air circulated into and recirculated within the building can pass over the bipolar emitting devices, which generally take the form of an ionization tube or tubes. This would accomplish the goal of improving air quality, without mandating greater air exchange rates. Thus, an additional benefit of ionization treatment of indoor air is that it contributes to the efficiency of HVAC operations.
In U.S. Pat. No. 1,793,799, issued to Hartman, a bipolar ionization tube is disclosed having a cathode formed by a metallic lining located along an interior surface of a glass tube. While the '799 patent discloses a wire mesh forming the anode, it does not suggest the use of a comparable wire mesh as the cathode. Rather, the '799 patent disclosed that the interior of a vacuum pumped glass tube be treated with the application, by brush, of a finely divided metal mixed with an adhesive. Neither the brushing and vacuum requirements are desirable manufacturing steps and the degree and interstitial spacing of the metal is random.
There is also a commercially available product sold under the Bentax™ trademark, which employs a tube assembled without vacuum pumping, and which uses a wire mesh for the cathode. It includes an open ended tube which is separately closed with an end cap. Although addressing some of the deficiencies of Hartman's bipolar ionization tube, the Bentax™ tubes are relatively fragile, have encountered numerous mechanical failures during shipping and due to mishandling, and stress-related failures at temperatures above 140° F.
Therefore, there is a need in the art for an improved, more efficient bipolar ionization tube with lower manufacturing costs, a reduced mechanical failure rate, and which can as a result be reduced in size and therefore be better adapted for installation in a wider range of HVAC systems or stand-alone devices.